Method and apparatus for surface hardening a component, which is made of an intermetallic compound at least in the region of the surface to be hardened

ABSTRACT

A method and apparatus for surface hardening a component, particularly an aircraft construction component, is disclosed. A force is applied to the surface of the component, which is made of an intermetallic compound at least in the region of the surface to be hardened. The component is heated at least in the region that is made of the intermetallic compound to a temperature higher than the standard temperature. The temperature is set such that a ductility of the intermetallic compound at the temperature is increased compared to a ductility of the intermetallic compound at the standard temperature. The apparatus includes a hardening tool and a heating device where the component is heated to a temperature higher than the standard temperature and the temperature is set such that a ductility of the intermetallic compound at the temperature is increased compared to a ductility of the intermetallic compound at the standard temperature.

BACKGROUND AND SUMMARY OF THE INVENTION

This application claims the priority of International Application No. PCT/DE2010/000522, filed May 8, 2010, and German Patent Document No. 10 2009 023 060.2, filed May 28, 2009, the disclosures of which are expressly incorporated by reference herein.

The invention relates to a method as well as an apparatus for surface hardening a component, particularly an aircraft construction part, which is made of an intermetallic compound at least in the region of the surface to be hardened.

The advantage of many intermetallic compounds such as, for example, TiAl alloys, is that they are relatively light, have good properties of strength and stiffness and withstand high working temperatures. Because of these properties, they are used as lightweight construction materials for certain components, in particular for components of aircraft engines and the like, and in doing so, are able to replace nickel alloys having substantially higher densities. The disadvantage, however, is that intermetallic compounds to some extent have ceramic properties and at room temperature are relatively brittle and sensitive to impacts. For strength reasons, compressive stresses close to the surface are desired in the case of components that are fabricated at least partially of such an intermetallic compound. To this end, the surface of the component must be hardened appropriately. The shot peening method and compact rolling method are known from the prior art as common methods for surface hardening these types of components.

However, the fact that local crack formation may occur in the component due to the comparatively high brittleness must be regarded as the disadvantage of this method for surface hardening. This results in a high level of spoilage and correspondingly high process costs.

The object of the present invention is creating a method as well as an apparatus of the type cited at the outset which makes possible an improved surface hardening of a component, which is made of an intermetallic compound at least in the region of the surface to be hardened.

Advantageous embodiments of the method are to be viewed as advantageous embodiments of the apparatus and vice versa.

A method according to the invention for surface hardening of a component provides that the component is heated at least in the region thereof that is made of the intermetallic compound to a temperature higher than the standard temperature, wherein the temperature is set such that a ductility of the intermetallic compound at the temperature is increased compared to a ductility of the intermetallic compound at the standard temperature. In this case, a temperature of T=298.15 K or T=25° C. should be understood as standard temperature. In other words, by heating the component or at least the region thereof made of the intermetallic compound that is to be hardened, the intermetallic compound is transformed into a more ductile state. A substantial reduction of and, in an ideal case, a complete avoidance of crack formation and other surface damage is hereby achieved with surface hardening. In addition, improved, deep-reaching hardening states as well as the formation of nanostructured structures in the intermetallic compound are produced, thereby also substantially improving the mechanical properties of the component. In addition, the method makes it possible to achieve great cost reductions, because the proportion of spoilage and unusable components is reduced significantly. In the process, it may be provided that the temperature is changed during the process singly and/or multiple times continuously and/or discontinuously in order to produce different ductility progressions. The method may be used both in the course of fabricating new parts as well and for repairs. For example, it is possible to harden components or component regions of gas turbines that are heavily stressed by friction wear or the like. Similarly, it is also possible to use this surface hardening method to minimize or eliminate to the greatest possible extent warping, material migration, butt joints or other defects.

An advantageous embodiment of the invention provides that the component is heated at least in the region thereof that is made of the intermetallic compound to a temperature over 80° C., in particular over 100° C., and/or to a temperature at which the ductility of the intermetallic compound is increased by at least 5%, in particular by at least 10%, as compared to its ductility at the standard temperature. This advantageously ensures that there is a sufficient increase in ductility as a function of the respective properties of the intermetallic compound in question and the incidence of crack formation is reduced or completely prevented in an especially reliable manner.

Further advantages are yielded if a component, whose intermetallic compound includes TiAl and/or is made of TiAl, is surface hardened. This makes it possible to produce the component in an especially easy manner with a high modulus of elasticity as well as with especially high strength and good resistance to oxidation and corrosion. In addition, the component produced and surface hardened in this way is creep resistant up to temperatures of 750° C., thereby making it particularly suitable for use as an aircraft component. In this case, it may be provided that the temperature at which the component is heated during surface hardening is selected and adjusted as a function of the respectively present intermetallic phase of the titanium aluminide.

A further advantageous embodiment of the invention provides that the component is surface hardened by a shot peening method, in particular by ultrasonic shot peening, and/or by a rolling method, in particular by compact rolling, and/or by an ultrasonic impact treatment (UIT) method. This makes an especially high level of flexibility and adaptability of the method to different intermetallic compounds and component types possible.

Another embodiment of the invention provides that the component is surface hardened with a hardening tool, wherein the hardening tool is heated to a temperature that is above standard temperature. In other words, both the component (in its entirety or at least the region thereof made of the intermetallic compound) and the hardening tool being used are heated, thereby preventing an undesired cooling of the component during surface hardening. The ductility that is increased by the heating is hereby retained during the method, thereby preventing damage to the component on the one hand, and achieving deep-reaching hardening states in the component on the other hand. At the same time, it may also be provided that the component or the region thereof to be hardened that is made of the intermetallic compound is heated by means of the hardening tool.

An especially reliable guidance of the process is achieved in a further embodiment in that the hardening tool and the component are heated to at least essentially the same temperatures. In this case, temperature differences of approximately ±10 K should be understood as essentially the same temperatures. The increase in ductility of the component may be adjusted hereby in an especially precise manner and be kept constant at the respectively adjusted parameter value during the entire method despite the application of force by the hardening tool.

It has been shown to be advantageous in a further embodiment if the hardening tool is heated by means of the inductive and/or electric heating device. Although heating devices with a burner or with heat radiation may also be used in principle, the component may be heated to the respective desired temperature especially simply, reliably and flexibly with the aid of an inductive and/or electric heating device. In particular, the use of an inductive heating device in this case allows a very short reaction time in the case of changes in the temperature setting and an easily controlled heat input to the component. In addition, the setting of different temperatures or a heating of the component that is controlled by a temperature program may be carried out hereby in an especially quick and precise manner. In addition, adjacent regions of the component are not heated or only heated negligibly.

By surface hardening the component in an inert gas atmosphere and/or at a pressure that is reduced as compared to the standard pressure, in particular in a vacuum, an undesired surface oxidation of the component is advantageously prevented. A pressure of p=1 atm or p=101325 Pa should be understood as standard pressure.

A further aspect of the invention relates to an apparatus for surface hardening a component, in particular an aircraft construction component. The apparatus comprises a hardening tool, by means of which a force can be applied to the surface of the component, which is made of an intermetallic compound at least in the region of the surface to be hardened. According to the invention, an improved surface hardening of the component is achieved in that the apparatus comprises a heating device, by means of which the component is heated at least in the region thereof that is made of the intermetallic compound to a temperature higher than the standard temperature, wherein the temperature is set such that a ductility of the intermetallic compound at the temperature is increased compared to a ductility of the intermetallic compound at the standard temperature. In this case, a temperature of T=298.15 K or T=25° C. should be understood as standard temperature. In other words, the component or at least the region thereof made of the intermetallic compound that is to be hardened may be heated with the aid of the heating device and the intermetallic compound is transformed to a more ductile state. A substantial reduction of and, in an ideal case, a complete avoidance of crack formation and other surface damage is hereby made possible with surface hardening. In addition, components with improved, deep-reaching hardening states as well as nanostructured structures in the intermetallic compound may be produced with the aid of the apparatus according to the invention, thereby also substantially improving the mechanical properties of the component. In addition, the apparatus makes it possible to achieve great cost reductions, because the proportion of spoilage and unusable components may be reduced significantly. In the process, it may be provided that the heating device is designed to change the temperature during the process singly and/or multiple times continuously and/or discontinuously in order to produce targeted ductility progressions. The preferred embodiments and further developments presented in conjunction with the method according to the invention as well as the advantages thereof apply correspondingly to the apparatus according to the invention.

An advantageous embodiment of the invention provides that the hardening tool comprises an armored hardening tool head, in particular a hardening tool head made of tungsten carbide and/or titanium nitride and/or boron nitride. This permits an especially efficient transmission of force from the hardening tool to the surface of the component almost independently of the material of the component as well as an associated high plastic deformation of the component material. In addition, the durability of the hardening tool or the hardening tool head is hereby advantageously increased. The use of tungsten carbide and/or titanium nitride and/or boron nitride in this case allows an especially high hardness and wear resistance of the hardening tool head.

Additional advantages are yielded if the apparatus comprises a hardening tool with a die-like hardening tool head and/or a peening chamber, in which at least the surface region of the component to be hardened can be arranged. A die-like hardening tool head makes it possible to produce a selective compression of the component material and therefore an especially deep-reaching compressive stress in a structurally simple manner and independent of the surface geometry. Alternatively or additionally, a peening chamber creates a simple possibility of hardening the surface region of the component in a targeted manner through the application of a peening medium. In this case, it may also be provided that the peening chamber is designed to be adapted to different types of components to be processed. To this end, the peening chamber may have a chamber wall with an adjustable wall region.

Another advantageous embodiment of the invention provides that the heating device include an induction coil. The component may be heated hereby to the respective desired temperature especially simply, reliably and flexibly manner with the aid of magnetic induction. An inductive heating device in this case allows a very short reaction time in the case of changes in the temperature setting and an easily controlled energy input to the component. In addition, the setting of different temperatures or a heating of the component that is controlled by a temperature program may be carried out hereby in an especially quick and precise manner. In addition, adjacent regions of the apparatus are not heated or only heated negligibly by secondary reheating.

Additional features of the invention are disclosed in the claims, the exemplary embodiments and the drawings. The features and combinations of features cited in the foregoing description as well as the features and combinations of features cited in the subsequent exemplary embodiments are not just applicable in the respectively indicated combination, but also in other combinations or alone without leaving the scope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective schematic diagram of a component made of an intermetallic compound, which is heated by means of an apparatus according to the invention for surface hardening and to which a force is applied; and

FIG. 2 is a schematic sectional view of another exemplary embodiment of the apparatus according to the invention for surface hardening.

DETAILED DESCRIPTION OF THE DRAWINGS

The same or functionally equivalent elements are provided with identical reference numbers in the drawings. FIG. 1 shows a perspective schematic diagram of component 10 made of an intermetallic compound, whose surface 12 is heated by means of an apparatus 13 according to the invention for surface hardening and to which a force is applied. The component 10 in the case at hand is configured as a gas turbine component for an aircraft and is made of TiAl. For surface hardening, a sonotrode-like hardening tool 14 of the apparatus 13 acts upon the surface 12 of the component, thereby producing a plastic deformation of the component 10 and local compressive stresses in the component 10. The hardening tool 14 in this case is excited in the ultrasonic frequency range, thereby producing a so-called ultrasonic impact treatment (UIT) of the component 10. The component 10 may basically be a new part of a used part or a used part, which, for example, may have a scratch or other damage as a surface defect 12 a. The repair reliably prevents the formation of a crack or propagation of a crack originating from a scratch. Alternatively or additionally, however, other surface defects 12 a may also be repaired such as, for example, local material non-homogeneities, unfavorable states of stress in the case of joining connections, cracks, depressions or the like in order to prevent the formation or propagation of cracks.

The component 10 at hand is designed to be thin-walled and is accessible only from one side. In contrast to the prior art, any possible backing (not shown) does not have to be removed to carry out the repair method, however. In addition, because of the high-frequency application of force (hammering) with the hardening tool 14, the thin-walled component 10 has enough inert mass to be hardened without rear support and with macroscopic deformation. Both a repair as well as a surface hardening of a new part may be carried out hereby in an especially quick and economical manner.

The hardening tool 14 whose basic structure is known from the prior art includes for its part an actuator 18, which causes a die-like hardening tool head 20 to oscillate in the ultrasonic frequency range. The hardening tool head 20, which is designed to be armored and has, for example, a tungsten carbide hemisphere 22 on its end region being used for impact, for its part transfers the oscillation energy to the surface 12 or to the defective surface region 12 a, thereby hardening the component 10 at the impact location. A hardening tool axis A running in the effective direction of the hardening tool 14 is arranged in the present example to be parallel to a surface normal of the surface 12 in the impact region. As an alternative or an addition, the hardening tool axis A may be arranged at an angle, in particular at an angle between 10° and 80°, to the surface normal of the surface 12 in the impact region in order to achieve preferentially oriented hardening states.

During the repair, the component 10 and the hardening tool 14 are moved relative to one another guided manually or mechanically. In the present exemplary embodiment, the component 10 remains stationary, while the hardening tool 14 is moved. This makes repairing the component 10 possible without it having to be dismantled. However, it may also be provided that the component 10 is held by means of a holding device (not shown). A T-slot table, for example, may be used as the holding device. Similarly, it may be provided that the component is held on the holding device by applying a negative pressure.

In order to prevent the occurrence of local crack formation in the component 10 during surface hardening due to the comparatively high brittleness of the intermetallic compound TiAl, the apparatus 13 includes a heating device 24 by means of which the component 10 is heated to a temperature higher than the standard temperature. The temperature in this case is set such that a ductility of the intermetallic compound at the temperature is increased as compared to a ductility of the intermetallic compound at the standard temperature. The heating device 24 for its part comprises an induction coil 26, which is operated by means of an allocated high-frequency generator (HF generator) 28. The heating device 24 in this case is arranged such that it heats both the hardening tool 14 as well as the surface 12 of the component 10 to a predetermined temperature. The heating device 24 in this case may be operated in a controlled and/or regulated manner, whereby the setting of different temperatures or the carrying out of a temperature program is made possible. Because of the operating principle of the ultrasonic impact treatments without compressed air, an undesired cooling of the component 10 is also advantageously prevented. In this case, it may be provided that the surface hardening method is carried out in a vacuum and/or in inert gas in order to prevent a surface oxidation of the component 10.

FIG. 2 shows a schematic sectional view of another exemplary embodiment of the apparatus 13 according to the invention for surface hardening. In contrast to the foregoing exemplary embodiment, as a hardening tool 14, the apparatus 13 comprises a peening chamber 32 filled with a peening medium 30 with a variable volume. The component 10 is arranged in sections within the peening chamber 32 and is surfaced hardened by ultrasonic shot peening. To this end, the peening medium 30 is excited by means of a sonotrode-like actuator 18 in a manner known per se in the ultrasonic frequency range and accelerated onto surface 12 of the component 10. The actuator 18 is activated for its part via a booster 34 and a piezo-electric drive 36, wherein the piezo-electric drive 36 is activated via an attached generator 38. The induction coil 26 of the heating device 24 is arranged inside the peening chamber 32 in the present example and heats both the component 12 and the peening chamber 32 and the peening medium 30. The HF generator 28 connected to the induction coil 26 is not depicted for the sake of providing a clearer overview. Alternatively, it is possible for the induction coil 26 to be arranged outside the peening chamber 32. Also in this case, the similar operating principle of ultrasonic shot peening without compressed air is responsible for preventing an undesired cooling of the component 10. In doing so, it is also possible in the present exemplary embodiment to provide for the surface hardening method to be carried out in a vacuum and/or in inert gas in order to prevent a surface oxidation of the component 10.

The parameter values indicated in the documents to define process conditions and measuring conditions for characterizing specific properties of the subject of the invention are to be viewed as included in the scope of the invention even in the context of deviations, e.g., due to measuring errors, system defects, weighing errors, German Industry Standards (DIN) tolerances and the like. 

1-13. (canceled)
 14. A method for surface hardening a component, comprising the steps of: applying a force to a surface of the component in a region wherein the component is made of an intermetallic compound; heating the component at least in the region to a temperature that is higher than a standard temperature; and setting the temperature such that a ductility of the intermetallic compound at the set temperature is increased compared to a ductility of the intermetallic compound at the standard temperature.
 15. The method according to claim 14, wherein the set temperature is over 80° C.
 16. The method according to claim 14, wherein the ductility of the intermetallic compound is increased by at least 5% compared to the ductility at the standard temperature.
 17. The method according to claim 14, wherein the intermetallic compound includes TiAl and/or is made of TiAl.
 18. The method according to claim 14, wherein the step of applying a force includes shot peening or rolling or ultrasonic impact treatment.
 19. The method according to claim 14, wherein the step of applying a force includes applying the force with a hardening tool, and further comprising the step of heating the hardening tool to a temperature that is higher than the standard temperature.
 20. The method according to claim 19, wherein the hardening tool and the component are heated to at least essentially a same temperature.
 21. The method according to claim 19, wherein the step of heating the hardening tool includes heating the hardening tool by an inductive and/or an electric heating device.
 22. The method according to claim 14, wherein the step of heating the component includes heating the component by an inductive and/or an electric heating device.
 23. The method according to claim 14, wherein the step of applying is performed in an inert gas atmosphere and/or with a pressure that is reduced as compared to a standard pressure.
 24. The method according to claim 14, wherein the component is an aircraft construction component.
 25. An apparatus for surface hardening a component, comprising: a hardening tool, wherein a force is applyable to a surface of the component; and a heating device, wherein the component is heatable by the heating device at least in a region of the surface that is made of an intermetallic compound to a temperature higher than a standard temperature and wherein the temperature increases a ductility of the intermetallic compound as compared to a ductility of the intermetallic compound at the standard temperature.
 26. The apparatus according to claim 25, wherein the hardening tool includes an armored hardening tool head.
 27. The apparatus according to claim 26, wherein the armored hardening tool head is made of tungsten carbide and/or titanium nitride and/or boron nitride.
 28. The apparatus according to claim 25, wherein the hardening tool includes a peening chamber, wherein the surface is arrangeable within the peening chamber.
 29. The apparatus according to claim 25, wherein the heating device is an electric and/or an inductive heating device.
 30. The apparatus according to claim 25, wherein the hardening tool includes a die-like hardening tool head. 